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Abstract Background Congenital heart disease (CHD) is the most common congenital anomaly. Almost 90% of isolated cases have an unexplained genetic etiology after clinical testing. Non-canonical splice variants that disrupt mRNA splicing through the loss or creation of exon boundaries are not routinely captured and/or evaluated by standard clinical genetic tests. Recent computational algorithms such as SpliceAI have shown an ability to predict such variants, but are not specific to cardiac-expressed genes and transcriptional isoforms. Methods We used genome sequencing (GS) (n = 1101 CHD probands) and myocardial RNA-Sequencing (RNA-Seq) (n = 154 CHD and n = 43 cardiomyopathy probands) to identify and validate splice disrupting variants, and to develop a heart-specific model for canonical and non-canonical splice variants that can be applied to patients with CHD and cardiomyopathy. Two thousand five hundred seventy GS samples from the Medical Genome Reference Bank were analyzed as healthy controls. Results Of 8583 rare DNA splice-disrupting variants initially identified using SpliceAI, 100 were associated with altered splice junctions in the corresponding patient myocardium affecting 95 genes. Using strength of myocardial gene expression and genome-wide DNA variant features that were confirmed to affect splicing in myocardial RNA, we trained a machine learning model for predicting cardiac-specific splice-disrupting variants (AUC 0.86 on internal validation). In a validation set of 48 CHD probands, the cardiac-specific model outperformed a SpliceAI model alone (AUC 0.94 vs 0.67 respectively). Application of this model to an additional 947 CHD probands with only GS data identified 1% patients with canonical and 11% patients with non-canonical splice-disrupting variants in CHD genes. Forty-nine percent of predicted splice-disrupting variants were intronic and > 10 bp from existing splice junctions. The burden of high-confidence splice-disrupting variants in CHD genes was 1.28-fold higher in CHD cases compared with healthy controls. Conclusions A new cardiac-specific in silico model was developed using complementary GS and RNA-Seq data that improved genetic yield by identifying a significant burden of non-canonical splice variants associated with CHD that would not be detectable through panel or exome sequencing.

Objective To examine associations between maternal immigrant status and survival of children with congenital heart disease (CHD). Approach A retrospective population-based cohort study of hospital live births between April 2002 to September 2020 in Ontario, Canada was conducted at ICES. We identified children aged 0-17 years with a diagnosis of CHD from inpatient and health services datasets. The exposure was maternal immigrant status obtained from the IRCC permanent resident database. The outcome was time-to-death from after birth to

Abstract Background This study aims to evaluate the impact of socioeconomic status (SES) on the risk of congenital heart disease (CHD) since previous studies have yielded inconsistent results. Methods We conducted a population-based retrospective cohort study, including all singleton live and still births in Ontario hospitals from April 1, 2012, to March 31, 2018. We used linked records from the Better Outcomes Registry & Network Information System, the Canadian Institute for Health Information databases, and the Ontario Marginalization Index (ON_Marg). ON_Marg was estimated at a dissemination area level using Canadian Census 2016 data and categorized into quintiles. Multivariable logistic regression models were performed to examine the relationships between four ON_Marg indices (material deprivation, dependency, ethnic concentration, residential instability), as proxies for maternal SES and the risk of infant CHD. We adjusted for maternal age at birth, assisted reproductive technology, obesity, pre-existing health conditions, substance use during pregnancy, mental health conditions before and during pregnancy, rural residence, and infant’s sex in the analysis. Results Among the cohort of 776,799 singletons, 9,359 infants had a diagnosis of CHD. Of those, 3,069 were severe CHD and 493 cases were single ventricle CHD. The prevalence of all infant CHD types was higher for males relative to females. Compared to mothers living in neighbourhoods with the lowest material deprivation, mothers with highest material deprivation had a 27% (adjusted OR = 1.27; 95% CI: 1.18–1.37) higher odds of having an infant diagnosed with CHD. Mothers living in neighbourhoods with the highest minority ethnic and immigrant concentration tend to have infants with 11% lower odds of CHD (adjusted OR = 0.89; 95% CI: 0.82–0.97) as compared to those living in the least ethnically diverse communities. Maternal dependency and residential stability quintiles were not significantly associated with the risk of CHD. Conclusion Higher maternal material deprivation was associated with increasing odds of infant CHD, whereas neighbourhood minority ethnic concentration was inversely associated with the odds of infant CHD. Our study further confirms that poverty is associated with CHD development. Future investigations might focus on the causal pathways between social deprivation, immigrant status, ethnicity, and the risk of infant CHD.

Objectives To enhance the confidence of children and adolescents with medical conditions and disabilities to engage in healthy, active lifestyles. Children with medical conditions and disabilities often exhibit more sedentary lifestyles relative to peers and are at increased risk of poor health outcomes. Clinical experience suggests physical activity confidence is an important factor influencing physical activity participation. Methods This randomized controlled trial evaluates an evidence-based intervention targeting physical activity confidence among children and adolescents with medical conditions and disabilities. Potential participants, 8 to 18 years of age diagnosed with a medical condition or disability, will be screened for adequate physical activity motivation but a lack confidence. Consenting participants (n=128) will be randomized 1:1 to a 12-week in-person or virtual physical activity intervention (24 hours/week total) led by a Registered Kinesiologist or control (assessments only). The intervention will combine physical activity participation with education about physical activity knowledge, goal setting, motivation and self-management. Primary outcomes are self-reported physical activity confidence and motivation at baseline, post-intervention and three months following intervention completion. A secondary outcome will be daily physical activity minutes assessed by accelerometry. A repeated measures mixed model will be used to compare outcomes between the in-person intervention, virtual intervention, and control groups (alpha=0.05). Conclusions This trial aims to assess the impact of a novel application of behaviour change theory on physical activity confidence among children and adolescents living with medical conditions or disabilities. Increased physical activity confidence, knowledge and skills could enable these youth to lead a more active lifestyle.

Abstract Background The risk of congenital heart disease (CHD) has been found to vary by maternal socioeconomic status (SES) and rural-urban residence. In this study, we examined associations of CHD with two maternal SES indicators and stratified the analysis by maternal rural-urban residence. Methods This was a population-based retrospective cohort study. We included all singleton stillbirths and live hospital births from April 1, 2012 to March 31, 2018 in Ontario, Canada. We linked the BORN Information System and Canadian Institute for Health Information databases. Multivariable logistic regression models were used to examine associations of CHD with material deprivation index (MDI), social deprivation index (SDI), and maternal residence while adjusting for maternal age at birth, assisted reproductive technology, obesity, pre-pregnancy maternal health conditions, mental health illness before and during pregnancy, substance use during pregnancy, and infant’s sex. MDI and SDI were estimated at a dissemination area level in Ontario and were categorized into quintiles (Q1-Q5). Results This cohort study included 798,173 singletons. In maternal urban residence, the p trend (Cochran–Armitage test) was less than 0.0001 for both MDI and SDI; while for rural residence, it was 0.002 and 0.98, respectively. Infants living in the most materially deprived neighbourhoods (MDI Q5) had higher odds of CHD (aOR: 1.21, 95% CI: 1.12–1.29) compared to Q1. Similarly, infants living in the most socially deprived neighbourhoods (SDI Q5) had an 18% increase in the odds of CHD (aOR: 1.18, 95% CI: 1.1–1.26) compared to Q1. Rural infants had a 13% increase in the odds of CHD compared to their urban counterparts. After stratifying by maternal rural-urban residence, we still detected higher odds of CHD with two indices in urban residence but only MDI in rural residence. Conclusion Higher material and social deprivation and rural residence were associated with higher odds of CHD. Health interventions and policies should reinforce the need for optimal care for all families, particularly underprivileged families in both rural and urban regions. Future studies should further investigate the effect of social deprivation on the risk of CHD development.

Abstract Cardiomyopathy (CMP) is a heritable disorder. Over 50% of cases are gene-elusive on clinical gene panel testing. The contribution of variants in non-coding DNA elements that result in cryptic splicing and regulate gene expression has not been explored. We analyzed whole-genome sequencing (WGS) data in a discovery cohort of 209 pediatric CMP patients and 1953 independent replication genomes and exomes. We searched for protein-coding variants, and non-coding variants predicted to affect the function or expression of genes. Thirty-nine percent of cases harbored pathogenic coding variants in known CMP genes, and 5% harbored high-risk loss-of-function (LoF) variants in additional candidate CMP genes. Fifteen percent harbored high-risk regulatory variants in promoters and enhancers of CMP genes (odds ratio 2.25, p = 6.70 × 10−7 versus controls). Genes involved in α-dystroglycan glycosylation (FKTN, DTNA) and desmosomal signaling (DSC2, DSG2) were most highly enriched for regulatory variants (odds ratio 6.7–58.1). Functional effects were confirmed in patient myocardium and reporter assays in human cardiomyocytes, and in zebrafish CRISPR knockouts. We provide strong evidence for the genomic contribution of functionally active variants in new genes and in regulatory elements of known CMP genes to early onset CMP.

Abstract Background This study aimed to examine the relationships between various maternal socioeconomic status (SES) indicators and the risk of congenital heart disease (CHD). Methods This was a population-based retrospective cohort study, including all singleton stillbirths and live births in Ontario hospitals from April 1, 2012 to March 31, 2018. Multivariable logistic regression models were performed to examine the relationships between maternal neighbourhood household income, poverty, education level, employment and unemployment status, immigration and minority status, and population density and the risk of CHD. All SES variables were estimated at a dissemination area level and categorized into quintiles. Adjustments were made for maternal age at birth, assisted reproductive technology, obesity, pre-existing maternal health conditions, substance use during pregnancy, rural or urban residence, and infant’s sex. Results Of 804,292 singletons, 9731 (1.21%) infants with CHD were identified. Compared to infants whose mothers lived in the highest income neighbourhoods, infants whose mothers lived in the lowest income neighbourhoods had higher likelihood of developing CHD (adjusted OR: 1.29, 95% CI: 1.20–1.38). Compared to infants whose mothers lived in the neighbourhoods with the highest percentage of people with a university or higher degree, infants whose mothers lived in the neighbourhoods with the lowest percentage of people with university or higher degree had higher chance of CHD (adjusted OR: 1.34, 95% CI: 1.24–1.44). Compared to infants whose mothers lived in the neighbourhoods with the highest employment rate, the odds of infants whose mothers resided in areas with the lowest employment having CHD was 18% higher (adjusted OR: 1.18, 95% CI: 1.10–1.26). Compared to infants whose mothers lived in the neighbourhoods with the lowest proportion of immigrants or minorities, infants whose mothers resided in areas with the highest proportions of immigrants or minorities had 18% lower odds (adjusted OR: 0.82, 95% CI: 0.77–0.88) and 16% lower odds (adjusted OR: 0.84, 95% CI: 0.78–0.91) of CHD, respectively. Conclusion Lower maternal neighbourhood household income, poverty, lower educational level and unemployment status had positive associations with CHD, highlighting a significant social inequity in Ontario. The findings of lower CHD risk in immigrant and minority neighbourhoods require further investigation.

OBJECTIVES This exploratory mixed-methods study explored the barriers to physical activity, daily physical activity and submaximal exercise capacity among children with and at risk for cardiomyopathy and children with atrial septal defects. METHODS The study followed a convergent parallel mixed methodology design. Semi-structured interviews explored physical activity barriers. Seven-day accelerometry assessed moderate-to-vigorous physical activity, and an intermittent cardiopulmonary exercise test measured submaximal exercise capacity. RESULTS Twenty children, including 5 with cardiomyopathy (n=2 females, 14.2 ± 2.7 years old), 7 who were genotype-positive phenotype-negative for cardiomyopathy (n=5 females, 10.6 ± 3.3 years old) and 8 with atrial septal defects (n=4 females, 9.4 ± 3.8 years old) were recruited. Children with cardiomyopathy reported disease-specific physical activity barriers, while children who were genotype-positive phenotype-negative perceived barriers related to lack of time, parent support or activity motivation. The average daily moderate-to-vigorous physical activity was less than the recommended 60-minutes/day (n=20, mean 48.1 ± 18.0 minutes). Children with cardiomyopathy participated a median of 141.2 [interquartile range (IQR): 98.8) minutes of light-intensity physical activity and a median of 55.6 (IQR: 34.6) minutes of moderate-to-vigorous physical activity. The average submaximal exercise capacity was low (n=16, 25.2 ± 5.7 mL/kg/min). Estimated submaximal exercise capacity, including metabolic equivalent (4.5 ± 3.1 METs), respiratory exchange ratio (median = 1.0, IQR: 0.09) and ratings of perceived exertion (median = 7, IQR: 5) at peak exercise suggest that children with cardiomyopathy appear to have the exercise capacity to participate in low-to-moderate intensity activities. CONCLUSIONS These novel data suggest that a diagnosis of cardiomyopathy may not preclude children from participating in a healthy, active lifestyle. However, they perceive disease-specific physical activity barriers and may require support to optimize their level of participation for optimal health.

Abstract Background The vast majority of children undergoing cardiac surgery have low vitamin D levels post-operative, which may contribute to greater illness severity and worse clinical outcomes. Prior to the initiation of a large phase III clinical trial focused on clinical outcomes, studies are required to evaluate the feasibility of the study protocol, including whether the proposed dosing regimen can safely prevent post-operative vitamin D deficiency in this high-risk population. Methods We conducted a two-arm, double-blind dose evaluation randomized controlled trial in children requiring cardiopulmonary bypass for congenital heart disease. Pre-operatively, participants were randomized to receive cholecalciferol representing usual care (< 1 year = 400 IU/day, > 1 year = 600 IU/day) or a higher dose approximating the Institute of Medicine tolerable upper intake level (< 1 year = 1600 IU/day, > 1 year = 2400 IU/day). The feasibility outcomes were post-operative vitamin D status (primary), vitamin D-related adverse events, accrual rate, study withdrawal rate, blinding, and protocol non-adherence. Results Forty-six children were randomized, and five withdrew prior to surgery, leaving 41 children (21 high dose, 20 usual care) in the final analysis. The high dose group had higher 25-hydroxyvitamin D concentrations both intraoperatively (mean difference + 25.9 nmol/L; 95% CI 8.3–43.5) and post-operatively (mean difference + 17.2 nmol/L; 95% CI 5.5–29.0). Fewer participants receiving high-dose supplementation had post-operative serum 25-hydroxyvitamin D concentrations under 50 nmol/L, compared with usual care (RR 0.31, 95% CI 0.11–0.87). Post-operative vitamin D status was associated with the treatment arm and the number of doses received. There were no cases of hypercalcemia, and no significant adverse events related to vitamin D. While only 75% of the target sample size was recruited (limited funding), the consent rate (83%), accrual rate (1.5 per site month), number of withdrawals (11%), and ability to maintain blinding support feasibility of a larger trial. Conclusions Pre-operative daily high-dose supplementation improved vitamin D status pre-operatively and at time of pediatric ICU admission. The protocol for a more definitive trial should limit enrollment of children with at least 30 days between randomization and surgery to allow adequate duration of supplementation or consider a loading dose. Trial registration ClinicalTrials.gov, NCT01838447 . Registered on April 24, 2013

Background Transplacental fetal treatment of immune‐mediated fetal heart disease, including third‐degree atrioventricular block (AVB III) and endocardial fibroelastosis, is controversial. Methods and Results To study the impact of routine transplacental fetal treatment, we reviewed 130 consecutive cases, including 108 with AVB III and 22 with other diagnoses (first‐degree/second‐degree atrioventricular block [n=10]; isolated endocardial fibroelastosis [n=9]; atrial bradycardia [n=3]). Dexamethasone was started at a median of 22.4 gestational weeks. Additional treatment for AVB III included the use of a β‐agonist (n=47) and intravenous immune globulin (n=34). Fetal, neonatal, and 1‐year survival rates with AVB III were 95%, 93%, and 89%, respectively. Variables present at diagnosis that were associated with perinatal death included an atrial rate

Abstract Background Assess process, uptake, validity and resource needs for return of actionable research findings to biobank participants. Methods Participants were prospectively enrolled in a multicenter biorepository of childhood onset heart disease. Clinically actionable research findings were reviewed by a Return of Research Results Committee (RRR) and returned to the physician or disclosed directly to the participant through a research genetic counselor. Action taken following receipt of this information was reviewed. Results Genetic data was generated in 1963 of 7408 participants. Fifty-nine new findings were presented to the RRR committee; 20 (34%) were deemed reportable. Twelve were returned to the physician, of which 7 were disclosed to participants (median time to disclosure, 192 days). Seven findings were returned to the research genetic counselor; all have been disclosed (median time to disclosure, 19 days). Twelve families (86%) opted for referral to clinical genetics after disclosure of findings; 7 results have been validated, 5 results are pending. Average cost of return and disclosure per reportable finding incurred by the research program was $750 when utilizing a research genetic counselor; clinical costs associated with return were not included. Conclusions Return of actionable research findings was faster if disclosed directly to the participant by a research genetic counselor. There was a high acceptability amongst participants for receiving the findings, for referral to clinical genetics, and for clinical validation of research findings, with all referred cases being clinically confirmed.

OBJECTIVES Children with congenital heart disease (CHD) often lack confidence and demonstrate limited movement skills during physical activity. Community-based sport programs have been suggested to build their confidence and competence. This study examined the feasibility and physical literacy impact of an existing community-based sport program for children with moderate to complex CHD. METHODS This pilot study employed a parallel mixed method, single-case experimental design to evaluate the feasibility and impact of a weekly, community-based sport intervention (Sportball©). Intervention field notes and focus group transcripts were analysed deductively to inform feasibility. Physical literacy outcomes were measured using the Canadian Assessment of Physical Literacy. Paired t-tests examined changes in physical literacy scores, while qualitative data informed perceived changes in physical literacy tasks. RESULTS Participants (n=11, 45% female) were 8.2 ± 1.2 years. Nine children completed >80% of the 1-hour Sportball© sessions (10 lessons total). No adverse events occurred during or as a result of the intervention. Enabling participants to recognize the sensations of exercise and whether or not they needed to rest, designing activities and instructions to mitigate the risk of body contact, and accommodating the needs of participants with developmental/attentional limitations were important factors embedded into the design of the program, contributing to its feasibility. Participants reported perceived improvements in movement skill and torso endurance/strength, changes which were reflected in the objective physical literacy measures (movement skill: ∆ mean= 2.0 ± 0.98 points, p=0.07, r=0.57; torso endurance/strength: ∆ mean= 5.27 ± 7.20 seconds, p=0.44, r=0.26). CONCLUSIONS The Sportball© intervention was feasible for children with CHD, including those with activity restrictions or developmental delays. Children enjoyed the program and wanted it to continue. Measurable improvements in movement skill and muscular endurance were recognized by participants. Future trials evaluating Sportball©’s impact with larger samples and multiple 10-week sessions are recommended.